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Infrared dental imagingRelated Patent Categories: Dentistry, Apparatus, Having Means To Emit Radiation Or Facilitate Viewing Of The WorkInfrared dental imaging description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070134615, Infrared dental imaging. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application 60/748,809, filed Dec. 8, 2005, that is incorporated herein by reference. TECHNICAL FIELD [0002] The disclosure pertains to methods and apparatus for using infrared light to create pictures of teeth for assessment and treatment. BACKGROUND [0003] X-ray imaging is useful in dentistry because it reveals information about the inside of a tooth. This includes cavities or voids in the dental tissue, and also includes demineralized areas where the mineral content of the tissue has been reduced and the tissue becomes porous, typically as a result of acid in contact with the tooth. X-ray imaging works because cavitated or demineralized areas are more transparent to x-rays than surrounding tissues, and therefore transmit a higher intensity of the x-rays emanating from a source, creating a greater exposure on photographic film or on an electronic imaging device than the exposure created by radiation coming along nearby paths that do not intercept cavitated or demineralized zones. Since x-rays travel in nearly straight lines through the tooth, imaging is generally accomplished, not by focusing with a lens, but by using a very small source for the x-rays, so that a graded shadow is produced on the film or electronic detector. The size of the source will determine the degree to which the image is sharp or blurry. [0004] X-ray imaging has several disadvantages. X-rays ionize molecules in living tissue and are therefore dangerous. The contrast in x-ray images of small caries is poor, because a small carious volume with increased transparency or reduced attenuation only makes a small fractional change in the intensity of transmitted radiation even if the carious region is perfectly transparent, as when it is void of matter. Interproximal caries (on the sides of teeth) can often be seen despite this disadvantage because x-rays from these caries come through relatively little matter near the edges of the tooth. Occlusal caries (on or just below the biting surfaces of molars) often cannot be seen at all, because these biting surfaces are generally broad and flat, so that the x-rays are transmitted through a large amount of matter which is quite opaque, and because the fractional change due to caries is small. It would be valuable to observe the lateral extent of occlusal decay by looking vertically through the biting surfaces of molars, but X-rays can generally only be used through the sides of teeth (traversing horizontally when the patient's head is upright). Even if x-rays could be used vertically, the opacity due to the long distance through the dental tissue would probably make this geometry ineffective for viewing the lateral extent of occlusal decay. [0005] In addition to the detection of caries, dentists need to detect cracks in teeth, particularly when replacing an old filling and deciding whether to apply another inlay (which is acceptable if there is no crack but problematic if there is one) or to apply a crown (which is indicated if there is a crack). But x-ray techniques are not reliable for detecting cracks. A crack may show if it happens to be aligned with the beam, but will not show at all if it is not aligned. [0006] Attempts have been made to use visible light for detecting dental anomalies. These techniques avoid ionizing radiation. Unlike x-rays, however, visible light does not travel straight through a typical thickness of dental enamel or dentin, but is scattered randomly in all directions. This makes teeth appear milky white, and prevents detection of deep anomalies because the scattering seriously blurs the light. A commercial product that records digital images made with light in the visible wavelengths has been shown to be quite ineffective for detecting and characterizing interproximal lesions in comparison to x-ray. See, for example, Young and Featherstone, "Comparing digital imaging fiber-optic trans-illumination, F-speed radiographic film, and polarized light microscopy," in Early Detection of Dental Caries. III: Proceedings of the 6th Annual Indiana Conference, G. K. Stookey, ed. (2003). This product can only detect anomalies that are on or very near the surface of the tooth, and cannot determine their depth or whether they have penetrated through the enamel and into the dentin, which is important for decisions on therapy. [0007] Imaging with infrared light can reduce the problems with x-rays and visible-light imaging because dental enamel is substantially more transparent to infrared light than to visible light. But methods that use infrared cameras present additional problems. This disclosure describes some of those problems and presents methods and apparatus that mitigate them in ways that are suitable for practical, widespread commercial use of infrared dental imaging. SUMMARY [0008] Representative dental imaging systems disclosed herein comprise an interrogation optical scanner configured to scan an optical interrogation beam across at least a portion of at least one tooth, wherein the optical interrogation beam is substantially transmissable into the at least one tooth so as to produce a dentally modulated optical flux. An optical detection system is situated to produce a detection signal associated with the dentally modulated optical flux received from the at least one tooth, and a signal processor is coupled to receive the detection signal and produce position-dependent picture information associated with the at least one tooth based on the detection signal. In some examples, the signal processor is coupled to receive one or more scanner signals associated with a position of the interrogation beam on the at least one tooth. In some examples, a light source is configured to generate the optical interrogation beam at a wavelength of, or in a range of wavelengths greater than about 800 nm. Generally wavelengths or wavelength ranges are selected so that an interior of a tooth can be interrogated. In other examples, the wavelength or range of wavelengths of the optical interrogation beam is between about 1000 nm and 1800 nm. Wavelengths or ranges of wavelengths between about 1250 nm and 1350 nm and between about 1500 nm and 1600 nm are convenient. According to further examples, the light source is a laser diode or a light emitting diode. [0009] According to representative examples, a modulator is configured to apply a modulation to the optical interrogation beam, wherein the signal processor is configured to identify the position-dependent picture information based on the applied modulation. The applied modulation can be a periodic modulation having a period that is less than approximately one dwell time of the interrogation beam, wherein the dwell time is a ratio of an interrogation beam width in a scanned direction divided by a speed at which the beam is scanned. In other representative examples, the applied modulation is at a frequency greater than the frequencies associated with the picture information or at a frequency distant from frequencies associated with interfering illumination such as ambient illumination. [0010] According to some embodiments, an optical filter is situated with respect to the detection system so as to preferentially direct or conduct optical radiation associated with an interaction of the optical interrogation beam and the at least one tooth to the detection system. In further examples, the optical detection system comprises a first optical detector and a second optical detector that are configured to produce a first optical detection signal and a second optical detection signal, respectively. In still further additional examples, the optical interrogation beam includes an optical flux in a first wavelength range and an optical flux in a second wavelength range, and the first optical detector and the second optical detector produce the first optical detection signal and the second optical detection signal based on the optical flux in the first wavelength range and the second wavelength range, respectively. [0011] In still other disclosed embodiments, the interrogation optical scanner includes a scan controller and an optical waveguide that has an output end configured to be selectively displaced in response to the scan controller, and the optical interrogation beam is associated with optical radiation exiting the output end of the optical waveguide. In a convenient example, the optical waveguide is an optical fiber. The interrogation optical scanner can include at least one rotatable mirror configured to scan the optical interrogation beam along at least one scan direction. [0012] According to some examples, a dental display scanning system can be provided that includes a display optical scanner that directs an optical display beam onto a display surface. A modulation of the optical display beam is selected so as to produce a visible image of the tooth associated with the dentally modulated optical flux. The visible image of the tooth produced by the optical display can be formed on a surface of the at least one tooth, or on an image screen situated in proximity to the at least one tooth, or at other locations. In a particularly convenient example, the display optical scanner and the interrogation optical scanner are based on a common optical beam scanner that receives both an interrogation optical flux for delivery to the tooth and a display flux for forming the visible image. In some examples, a visible image is displayed that is based on a currently detected dentally modulated optical flux while in other examples a stored image is used. [0013] In additional examples, an optical coupling device or radiation collector is configured to couple the dentally modulated optical flux to the optical detection system. The optical coupling device can include an imaging optical system situated to image a surface of the at least one tooth at the optical detection system or can include a light guide situated to direct the dentally modulated optical flux to the optical detection system. An optical coupling device can be considered to be either part of the optical detection system, or a separate element. [0014] Dental imaging devices comprise an optically transmissive coupling surface having a predetermined surface shape and an optically transmissive conformable material in optical communication with the coupling surface, wherein the conformable material is configured to be conformable to a surface of a tooth. In representative examples, the coupling surface is provided on the conformable material. In additional examples, the coupling surface is provided on an optical window, and the conformable material contacts the optical window. The conformable material may be a fluid, a gel or a flexible solid, or a combination of theses. For purposes of this disclosure, "fluid" can include a gel or other material that can flow under sufficient pressure but maintains its shape under the mere force of gravity. Typically the predetermined surface shape of the coupling surface is substantially planar, but other surface shapes can be used. According to representative examples, a magnitude of a difference in an index of refraction of the conformable material and a refractive index of the tooth is less than a difference in the refractive index of the tooth and 1. In some examples, an index matching material can be applied to a tooth to reduce image contributions associated with surface features or to improve image contrast. [0015] Dental imaging methods comprise scanning an interrogation beam on at least a portion of a tooth so as to produce a dentally modulated optical flux associated with the interior of the tooth, and processing the dentally modulated optical flux to obtain an image of the tooth. In some examples, the interrogation beam consists essentially of optical radiation at wavelengths between about 1000 nm and 1800 nm. In additional examples, the interrogation beam is directed to the tooth through an index matching material such as a fluid or gel applied to the tooth. In alternative embodiments, the index matching material is a solid material that is conformed to the tooth surface. In some embodiments, an image of the tooth is formed in proximity to the tooth based on the dentally modulated flux. In other examples, the image of the tooth is formed on a surface of the tooth. [0016] In additional representative methods, scanning the interrogation beam comprises scanning a first interrogation beam and a second interrogation beam at a first wavelength and a second wavelength, respectively. Corresponding dentally modulated optical fluxes are processed to form at least one image of the tooth. In some examples, the first interrogation beam and the second interrogation beam are scanned substantially simultaneously on the tooth. In a convenient example, an optical interrogation beam and a display beam are scanned with a common scanner. In additional examples, at least one marker is provided on or near a tooth surface so as to provide a depth indication in the image. [0017] Dental imaging systems comprise an optical system configured to produce at least a first image and second image associated with an interior of a tooth viewed from respective positions or directions, and at least one marker situated at or near a surface of the tooth and positioned so as to provide an indication of depth based on the first image and the second image. In some examples, the at least one marker is provided on a surface of a tooth. In other examples, the at least one marker is provided on a light coupling device. [0018] The above examples are representative of some features of the disclosed technology. These and other features and aspects of the disclosed methods and apparatus are set forth below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0019] FIG. 1 is a schematic diagram showing a dental imaging system that includes an optical scanner that scans a focused interrogation optical beam through an interior of a tooth. 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